YSICS: Troubleshooting an Equation Plot Issue

[zhillyz]

TL;DR

Copied equations from paper into MATLAB and gave some test variables but output looks weird

First image showing script and plot

Second image where all I have done is slightly change the thickness and now the plot looks very weird.

Final image showing the kind of plot I am expecting.

Am I just doing something stupid as I can't see what is wrong/different between my equations and the ones in the publication?
Here is the paper: https://iopscience.iop.org/article/10.1088/0022-3735/16/12/023/pdf
Any help of pointers would be appreciated.
PH

 

[SpinFlop]

They clearly have a typo in their definition of C since there are two opening parenthesis, but only one closing. My guess is that it should be $2(n^2 - 1)(n^2 - s^2)$. Try that and see if it fixes the problem.